The systematic assessment of drug effects in humans using combined measurement of cognitive functioning and brain electrophysiology is a powerful emergent technology. These methods have not been fully exploited in studies of the effects of diazepam or alcohol, two drugs which are commonly abused and often taken together. During this 5-year study of acute dose effects of diazepam and alcohol, jointly acquired behavioral and electrophysiological data will be used to: 1) determine the condition of afferent and efferent pathways, and the cognitive interface between them, 2) identify and localize impairments of specific information- processing operations within the cognitive reaction process, and 3) assess dose-related changes in performance strategies and in the management of cognitive resources. Speed loading and incentive variables will be used to test hypotheses about the mobilization and allocation of energetic resources. These experiments will result in a hierarchically integrated characterization of dose effects of diazepam and alcohol, independently and in combination, on cognition, sensory, motor and electrophysiological functioning in healthy young men. This will provide basic concepts, techniques and a comprehensive data base, with potential application to the systematic assessment of other benzodiazepines as well as other classes of drugs. The resulting account of the dose effects of diazepam and alcohol will fill major gaps in existing knowledge of the independent and combined effects of these drugs on information processing. The results will have predictive generality to the extent that stimulus input processing and response output processing are ubiquitous to most of the cognitive reaction processes invoked by the discrete performance demands encountered in daily human activities.